Electrical generator or motor structure – Dynamoelectric – Linear
Patent
1995-04-12
1997-12-23
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Linear
310 12, H02K 3318
Patent
active
057010404
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a magnet arrangement, to a drive device incorporating the magnet arrangement, and to cooling apparatus incorporating the drive device.
The invention relates more particularly to a drive device of the "loudspeaker" type, incorporating a magnet arrangement comprising a right circularly cylindrical permanent magnet, and a circularly cylindrical soft iron yoke which includes a pair of poles defining an annular magnet pole gap. The drive device incorporating this magnet arrangement includes an annular coil which can cooperate with the pole gap and which is powered by an alternating current to reciprocate the coil relative to the magnet arrangement.
Such a drive device may be utilised in loudspeakers or some types of linear motors, but a particularly important use is in Stirling Cycle cooling devices. Stirling Cycle coolers are particularly useful for refrigeration in environments, such as outer space, where a low weight, high reliability device is required. A typical use would be for cooling the sensor (and possibly the optics) of an infrared camera. Other possible uses of such a cooler are in cooling superconducting devices such as SQUIDS and in reliquefying the helium in Magnetic Resonance Imaging Machines.
A magnet arrangement, drive device and cooling apparatus of the above type are known from International Patent Application No. PCT/GB90/00592. FIG. 1 of this document discloses a conventional loudspeaker type drive device. It will be noted that the yoke comprises an upper disc-shaped member fixed to one face of the disc-shaped permanent magnet and a member which is "c"-shaped in cross-section, the central portion of the "c" being disc-shaped and fixed to the other face of the magnet, the outer limbs of the "c" extending outwardly beyond the periphery of the magnet, upwardly and finally inwardly to define an annular pole gap with the periphery of the upper member.
Whilst such a drive device operates satisfactorily, it would be desirable to produce a device of considerably higher power but of similar weight and size. Especially for outer space applications, higher power and low weight are paramount considerations; power on board a spacecraft is severely limited, as is payload capacity.
U.S. Pat. No. 4,075,517 (ADLER) describes a linear motor for disk drives arranged so that several disks can be accessed using the same motor system. Several loudspeaker coils are arranged concentrically between the poles of a conventional loudspeaker drive. The spaces between the coils are filled with ferromagnetic annular poles to keep the magnetic field lines under control across what would be a large air gap. No references is made about the efficiency of the system.
DE-A-3032308 (Yeda Research and Development Company) appears to be a vibration free compressor. FIG. 3 shows an arrangement consisting of two outer and two inner radially magnetised permanent magnets. Soft iron annuli are used inside and outside the permanent magnets in order to channel the flux. Two connected drive coils are used to take advantage of the flux reversal from the top half of the permanent magnet circuit to the bottom half. This linear drive would be difficult to manufacture as the radially magnetised magnets would have to be segmented. The flux reversal between the top and bottom halves of the magnet would cause problems with the field strength and direction.
EP-A1-0494653 describes a linear actuator suitable for a cryogenic cooler. The arrangement comprises first and second pistons arranged to reciprocate within a cavity, the axes of the two pistons being colinear. Each piston has an associated electro-magnet. The magnetic flux distribution may not be spatially constant.
The present invention differs from the arrangement described in EP-A1-0494653, in that it comprises spaced magnets between whose poles is a uniform magnetic flux distribution. This occurs partly as a result of magnetic ballast/shielding provided by a precisely dimensioned yoke. Thus superior control of axial displacement of a drive shaft is achievable. F
REFERENCES:
patent: 3896319 (1975-07-01), Chari
patent: 4075517 (1978-02-01), Adler
patent: 4603270 (1986-07-01), Van Davelaar
patent: 5434458 (1995-07-01), Stuart et al.
Patent Abstracts of Japan, vol. 4, No. 109 (E-20) (591) 6 Aug. 1980 & JP,A 55 066 264 (Sawafuji Denki) 19 May 1980--See abstract.
Baynham David Elwyn
Bradshaw Thomas William
Orlowska Anna Helena
British Technology Group Limited
Dougherty Thomas M.
Mullins B.
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